Process for removing enamel



252. cemeesmcus.

in no way in ured by Cross Reference Patented May 28,1929.

UNITED STATES PATENT OFFICE.

HARRY O. LANG, 01 PONTIAC, MICHIGAN.

PROCESS FOR REMOVING ENAMEL.

No Drawing.

The invention relates to a process for removing non-vitreous enamel from metals, and is particularly applicable for the salvaging of articles having a defective coating, since, according to th1s process, the metal 1s the treatment and the articles can be re-enameled without further preparation.

The process is particularly applicable also for use in removing baked or air dried enamels which usually have an asphaltum base, although the process may also be used in removing the coatings having a pyroxylin base. According to the present practice, the enamel is removed-by subjecting the article to a boiling caustic solution, or it is immersed in molten caustic soda; but in each of" these processes there are many disadvantages, among which are the injurious effects of the caustic upon the metal base, and, when using the latter process, the excessive temperature to which the metal is subjected has a tendency to warp the metal out of shape.

According to my improved process the enameled metal article is immersed in a bath of a molten metal salt at a temperature high enough to liquify the enamel so that it will separate from the metallic article, and, being of lesser specific gravity than the bath, will rise'to the top thereof and as soon as exposed to the atmosphere will be destroyed by burning. The temperature at which the bath is maintained dgpends upon the melting point of the ename 700 Fahrenheit up; but I have found that when utilizing the temperature of substantially 975 Fahrenheit, the removal of the enamel may be accomplished very quickly and this, therefore, appears to be a desirable temperature for commercial work.

The material used "for the bath preferably has a melting point below that of the enamel and should have a gravity greater than the enamel and less than the metallic base, so that the article when immersed will remain below the surface of the li uid until the action is complete. It is also esirable and may range from.

' Application filed May 19, 1924. Serial No. 714,482.

that the bath should have no chemical effect upon the metallic base. While there are a great many materials which might answer the above requirements, I have found that from a practical standpoint, considering the cost of the materials as well as their effectiveness in producing the desired results, that the following materials are entirely satisfactory: Sodium nitrate, potasslum nitrate, sodium mtrite, OIjJLX COIIIblIlflt-IOII df'afiy of said materials.-

"I'ii' carrying out the rocess the metallic salt is laced ina suitahlepot or container and raised to the desired temperature at which the material is in the molten condition. The enameled article is then immersed in the bath for a short period of time, whereupon the enamel separates from the metallic base, rises to the surface of. the liquid and is oxidized, thereby maintaining the bath free from any substantial amount of impurities. The article is then withdrawn from the bath and preferably is quenched in water to dissolve the adhering salt. Preferably the quenching bath consists of hot water so that on removal of the article therefrom the heat remaining in the metal will quickly evaporate the moisture and provide a dry surface that is immediately ready for reenameling without any further preparation.

Examiner 1 As an example of the process, it may be stated that by' maintaining the temperature of the salt bath at approximately 975 F. the time for removing a enamel is approximately one minute.

-l-Vhat I cIaim as my invention is:

1. A rocess for removing non-vitreous enamel rom a metallic base consisting in immersing the enameled article in a bath of a molten material comprising principally an alkali metal salt of nitric or nitrous acids.

2. A rocess for removing non-vitreous enamel rom a metallic base consisting in immersing the enameled article in a bath of a molten material comprising principally an alkali nitrate and an alkali nitrite. I

In testimony whereof I aflix my signature.

HARRY O. LANG.

four-coat baked 

